Although this method addresses itself to the packaging of cheese curds, it is also applicable to the packaging of perishable foods, or any other product one may wish to vacuum package.
Prior methods of vacuum packaging cheese do not provide a one step method for evacuating the air from a package of cheese, while knitting the curds and compacting the cheese, and simultaneously sealing the package.
The present method for vacuum packing cheese curds is to place the cheese in a plastic bag which is contained by a rigid container. With the open end of the bag folded down on top of the cheese product, a cover is clamped on the rigid container and the container is placed in a vacuum chamber and subjected to a vacuum. After a vacuum is achieved and the container is removed from the vacuum chamber, the cover is removed, the plastic bag is unfolded and the open end is flared. A clamping mechanism is applied to the flared open end to hold the sides of the bag together in a flat manner. A vacuum nozzle is placed in the bag and a vacuum is applied to the product to remove the air which reentered the bag when it was opened. The bag is then sealed.
The first vacuum causes the cheese curds to knit, this step takes place in the vacuum chamber. The second vacuum, which is applied outside the vacuum chamber, is to form a vacuum in the bag prior to the final seal.
A search of the U.S. Patents developed the following patents on vacuum packaging:
U.S. Pat. No.: 2,541,674, U.S. Pat. No.: 2,708,067, U.S. Pat. No. 3,108,881, U.S. Pat. No.: 3,149,772, U.S. Pat. No.: 3,261,140.
The closest known patent to the present invention is U.S. Pat. No. 3,108,881, issued to Shaw. The method used by Shaw to package foods includes a tortuous vent passage and heat to vaporize a liquid in the package to purge the air. The package is cooled to condense the vapor, forming a temporary seal and collapsing the package. Afterwards, the package is heat sealed to prevent ingress of air. The basic differences in the Shaw method and the present invention is the use of heat to vaporize the liquid and the manner of heat sealing the package. In the present invention, no heat is used since certain products will not tolerate heat without undergoing changes. The method of heat sealing the package in the present invention insures a complete seal, whereas the seal in the Shaw package is along one of the interrupted bend lines forming the tortuous vent passage.
There are at least two well known methods of forming vacuum packages which are worth mentioning as background to the present invention. The first method employs a flexible package in which the product is placed where the open end of the package closes around a vacuum probe. Gases are evacuated from the package through the probe, which is removed and the package heat sealed.
In the other accepted method, filled packages are placed in a vacuum chamber and the container is closed. After the chamber is evacuated, the packages are remotely sealed while still in the chamber and then the chamber is opened. The problem with this method is two fold: (1) the equipment for remote sealing is expensive, and (2) the quality control of the seals would be difficult to regulate.